Blacksburg, VA (CBS/AP) - A day after the deadliest shooting in U.S. history, the campus of Virginia Tech came together to remember the victims and heal the wounds created by Monday's massacre.

On Tuesday afternoon, thousands of people gathered in the Virginia Tech basketball arena, and when it filled up, thousands more filed into the football stadium, for a memorial service for the victims.

"We have come together today to remember the cherished and innocent members of the Virginia Tech family whose lives were so abruptly ended in the senseless act," said Zenobia Hikes, vice president of student affairs.

"We will eventually recover, but we will never, ever forget."

President Bush was in attendance and offered his sympathies to the campus.

"On this terrible day of mourning it's hard to imagine a time will come when life at Virginia Tech will return to normal," Mr. Bush said. "But such a day will come."

Virginia Gov. Tim Kaine applauded Virginia Tech students for the unity they displayed throughout Monday's chaos.

"Before it was about who was to blame or what could have been done different, it was about how do we take care of each other," Kaine said.

Virginia Tech President Charles Steger received a 30-second standing ovation, despite bitter complaints from parents and students that the university should have locked down the campus immediately after the first burst of gunfire. Steger expressed hope that "we will awaken from this horrible nightmare."

Meanwhile, a chilling portrait of the gunman began to emerge.

Police identified Cho Seung-Hui as the shooter who carried out the massacre that left 33 people dead, including himself. He was an English major whose creative writing was so disturbing that he was referred to the school's counseling service.

"He was a loner, and we're having difficulty finding information about him," school spokesman Larry Hincker said.

Police and university officials still offered no clues as to exactly what set off Cho, a 23-year-old senior, on the deadliest shooting rampage in modern U.S. history.

News reports said that he may have been taking medication for depression, that he was becoming increasingly violent and erratic, and that he left a note in his dorm in which he railed against "rich kids," "debauchery" and "deceitful charlatans" on campus. Cho arrived in the United States as a boy from South Korea in 1992 and was raised in suburban Washington, D.C., officials said. He was living on campus in a different dorm from the one where Monday's bloodbath began.

Professor Carolyn Rude, chairwoman of the university's English department, said she did not personally know the gunman. But she said she spoke with Lucinda Roy, the department's director of creative writing, who had Cho in one of her classes and described him as "troubled."

"There was some concern about him," Rude said. "Sometimes, in creative writing, people reveal things and you never know if it's creative or if they're describing things, if they're imagining things or just how real it might be. But we're all alert to not ignore things like this."

She said Cho was referred to the counseling service, but she said she did not know when, or what the outcome was. Rude refused to release any of his writings or his grades, citing privacy laws.

Receipts found in the gunman's backpack allowed authorities to trace one of the two handguns used in the shootings, though the serial numbers for both weapons were wiped clean, CBS News reports. Cho carried a 9 mm handgun and a 22 mm handgun during the shootings, police said.

One of the guns used in the massacre, the 9 mm semi-automatic Glock 19, was purchased brand new at a Roanoke, Va. gun shop, Roanoke Firearms, 36 days ago, CBS News has learned.

According to store owner John Markell, Cho paid roughly $570 on his credit card for the gun and a box of 50 rounds of ammunition used primarily for target practice.

Cho killed at least 30 people locked in a classroom.

Ballistics tests found that one of the guns used in that attack was also used in a shooting two hours earlier at a dorm that left two people dead, Virginia State Police said.

Col. Steve Flaherty, superintendent of the Virginia State Police, said it was reasonable to assume that Cho was the shooter in both attacks but that link was not yet definitive.

"There's no evidence of any accomplice at either event, but we're exploring the possibility," he said.

A note was found in Cho's dorm room, the Chicago Tribune reported, which included a list of grievances and rantings against "debauchery" on campus.

The gunman's furious shooting rampage Monday at Virginia Tech has left the school living a nightmare — shocked and horrified over the deaths of 32 students and teachers and wondering how such a massacre could occur.

Twelve people remained hospitalized in stable condition, a Virginia hospital spokesman said Tuesday.

All classes for the remainder of the week have been canceled, Virginia Tech President Charles Steger said.

Steger spent Tuesday morning defending the delay in warning students about the gunman. Some students said their first warning came more than two hours after the first shooting, in an e-mail at 9:26 a.m. By then the second shooting had begun.

"I can understand the anger and the rage," Steger told CBS' The Early Show. But Steger added bluntly, "We believe we have acted appropriately."

Some students bitterly complained they got no warning from the university until an e-mail that arrived more than two hours after the first shots.

The e-mail had few details. It read: “A shooting incident occurred at West Amber Johnston earlier this morning. Police are on the scene and are investigating.” The message warned students to be cautious and contact police about anything suspicious.

"I think the university has blood on their hands because of their lack of action after the first incident," said Billy Bason, 18, who lives on the seventh floor of the dorm.

Student Maurice Hiller said he went to a 9 a.m. class two buildings away from the engineering building, and no warnings were coming over the outdoor public address system on campus at the time.

Everett Good, junior, said of the lack of warning: “I'm trying to figure that out. Someone's head is definitely going to roll over that.”

Steger said the university was trying to notify students who were already on-campus, not those who were commuting in.

Steger said authorities believed the shooting at the dorm was a domestic dispute and mistakenly thought the gunman had fled the campus.

"We had no reason to suspect any other incident was going to occur," he said.

Steger emphasized that the university closed off the dorm after the first attack and decided to rely on e-mail and other electronic means to spread the word, but said that with 11,000 people driving onto campus first thing in the morning, it was difficult to get the word out.

President Bush has ordered flags to be flown at half staff until Sunday evening for the victims.

The shooting began about 7:15 a.m. on the fourth floor of West Ambler Johnston, a high-rise coed dormitory where two people died.

Police were still investigating around 9:15 a.m., when a gunman wielding two handguns and carrying multiple clips of ammunition stormed Norris Hall, a classroom building a half-mile away on the other side of the 2,600-acre campus.

At least 15 people were hurt in the second attack, some seriously. Many found themselves trapped after someone, apparently the shooter, chained and locked Norris Hall doors from the inside.

Students jumped from windows, and students and faculty carried away some of the wounded without waiting for ambulances to arrive.

SWAT team members with helmets, flak jackets and assault rifles swarmed over the campus. A student used his cell-phone camera to record the sound of bullets echoing through a stone building.

Inside Norris, the attack began with a thunderous sound from Room 206 — "what sounded like an enormous hammer," said Alec Calhoun, a 20-year-old junior who was in a solid mechanics lecture in a classroom next door.

Screams followed an instant later, and the banging continued. When students realized the sounds were gunshots, Calhoun said, he started flipping over desks to make hiding places. Others dashed to the windows of the second-floor classroom, kicking out the screens and jumping from the ledge of Room 204, he said.

"I must've been the eighth or ninth person who jumped, and I think I was the last," said Calhoun, of Waynesboro, Va. He landed in a bush and ran.

Calhoun said that the two students behind him were shot, but that he believed they survived. Just before he climbed out the window, Calhoun said, he turned to look at his professor, who had stayed behind, apparently to prevent the gunman from opening the door.

The instructor was killed, Calhoun said.

The gunman first shot the professor in the head and then fired on the class, another student, Trey Perkins, told The Washington Post.

"Everyone hit the floor at that moment," said Perkins, 20, of Yorktown, Va., a sophomore studying mechanical engineering. "And the shots seemed like it lasted forever."

Among the dead were professors Liviu Librescu and Kevin Granata, said Ishwar K. Puri, the head of the engineering science and mechanics department.

Librescu, an Israeli, was born in Romania and was known internationally for his research in aeronautical engineering, Puri wrote in an e-mail to The Associated Press.

Also killed was Ryan Clark, a student from Martinez, Ga., who had several majors and carried a 4.0 grade-point average, said Vernon Collins, coroner in Columbia County, Ga.

His friend Gregory Walton, a 25-year-old who graduated last year, said he feared the nightmare had just begun.

"I knew when the number was so large that I would know at least one person on that list," said Walton, a banquet manager. "I don't want to look at that list. I don't want to.

"It's just, it's going to be horrible, and it's going to get worse before it gets better."

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